Hot isostatic pressing is a processing technique in which high isostatic pressure is applied to a powder material contained in a sealed and evacuated canister at a high temperature. During the hot isostatic pressing cycle, the canister collapses as a result of the high gas pressures and high temperatures applied and results in consolidation of the powder material to form the article.
The powder material and canister for containing the powder material are typically formed of a metal, metal alloy, ceramic or ceramic-metallic. The canister may be formed by machining or by welding sheet metal. It may be built up by galvanic or sprayed metal deposition on a wax or polymeric form which is subsequently removed.
The canister may be filled with the powder material using a pipe extending between a powder material reservoir/hopper and an opening in the canister (typically in the upper surface of the canister). In order to avoid clogging, bridging or “rat-holing” of the powder material, a large diameter pipe is required.
Prior to sealing the canister in preparation for hot isotactic pressing, it is known to apply a vacuum to the chamber to remove gas and/or moisture entrained within the powder material in order to minimise any voids in the finished article. Again, a large diameter pipe is desirable to facilitate evacuation.
One problem with using a large diameter filling/evacuation pipe is that the weld/crimp between the pipe and the canister is vulnerable to failing (e.g. fracturing) during hot isostatic pressing. Another problem is that large diameter pipes collapse in an unpredictable manner and thus the forces on the weld/crimp between the pipe and canister are unpredictable.
It is known to provide a number of smaller diameter pipes rather than a single larger diameter pipe but this complicates the manufacturing process as an increased number of welds/crimps need to be formed between the pipes and canister and the increased number of joins increases the number of possible failure locations during the hot isostatic pressing.
The pipes for powder material filling/gas evacuation are typically welded or crimped to the canister prior to filling/evacuation and are left in place during the hot isostatic pressing during which they collapse. The collapsed pipes are machined from the canister after hot isostatic pressing.
Accordingly the present invention seeks to provide a pipe, an apparatus and a method for filling/evacuating a container that reduces some of the problems associated with the known pipes/methods.